Atrial Natriuretic Peptide in the Preterm Newborn

Atrial natriuretic peptide (ANP), plasma renin and renin substrate concentrations (PRC and PRS) were measured in 31 preterm infants with idiopathic respiratory distress syndrome. Infants were studied at a mean of 1.4 days; 17 infants were also studied 2 days later. A 6-hour urine collection was made from 13 male infants on the first day of sampling to assess renal function. Both ANP and PRC were elevated and showed wide ranges of values (geometric means of 620 pg/ml and 18.4 ng/ ml/h). Plasma ANP was significantly correlated with pH, PaCO₂ and base excess. No correlations with parameters of cardiovascular or renal function were found. Plasma ANP rose in 13 of the 17 paired samples. We suggest that the very high ANP concentrations in these babies are a consequence of the pulmonary haemodynamic disturbances which accompany respiratory distress in the newborn.